1. Field of the Invention
The present invention generally relates to a device in rock drilling machines with a gripping device which is rotatably mounted in a non-rotating drilling head and is intended to grip a drill string for transmitting rotational and axial movement to the string, and more specifically to the mounting of the gripping device in the drilling head.
2. Description of the Prior Art
Different rock drilling methods set different demands on rotational speed and feed force applied to the drill string. In diamond drilling, for example, high rotational speeds and relatively small feed forces are used (500-2000 r.p.m. and 5-20 kN), while low speeds and large feed forces (50-200 r.p.m. and 50-200 kN) are used for drilling with roller bits. Another method is percussion drilling.
These different methods place different demands, particularly on the thrust bearing between the drilling head and the gripping device, which are difficult to meet in one and the same structure.
The U.S. Pat. No. 3,565,187 teaches a pressurized medium activated gripping device which is rotatably mounted in a drilling head. The mounting comprises rolling bearings which take up both axial and radial forces which are propagated to the drilling head and gripping device via the drill string.
Typical for rolling bearings is sensibility to shock stresses, and therefore in the known structure one has had to use special rubber dampers if percussion drilling has to be carried out. Neither can the bearings take up large axial loads, particularly not in combination with high rotational speeds.